The present invention relates to an automated peening tool for automatically peening the tenons of cover plates to secure the cover plates and adjacent tips of turbine buckets to one another and to methods for peening the tenons for connecting the cover plates and buckets to one another.
In the construction of turbines, for example, steam turbines, cover plates are employed for a variety of reasons and are generally secured to the tips of the turbine buckets by peening tenons formed on the buckets or the cover plates. While radial peening is oftentimes used in certain bucket constructions, axial entry-type buckets are typically continuously coupled to one another by cover plates located between sides or side faces of adjacent bucket tips. The cover plates and bucket tips are conventionally alternately exposed about the periphery of the turbine wheel. Each cover plate typically has a pair of tenons projecting from opposite sides and extending through pairs of openings in the respective tips of adjacent buckets. Thus, a cover plate is secured to one bucket along one side of the cover plate and to another adjacent bucket along the opposite side of the cover plate with the pairs of tenons engaging through openings in the respective bucket tips. That is, each bucket tip has four openings and receives a pair of tenons of a cover plate on one side of the bucket tip through two of the openings and another pair of tenons of another cover plate on an opposite side of the bucket tip through the remaining two openings. It will be appreciated that there are other bucket/tip/cover plate securements having only one tenon for securing each bucket.
To secure the bucket tips and cover plates to one another, solid tenons on the admission sides of the cover plates are peened into the bucket tip openings in order to fill the entire chamfer machined about the bucket tip openings. Filling this chamfer pulls the bucket tight to the cover plate, enabling the cover plate and bucket to act as one integral assembly. The opposite side of each cover plate has a pair of hollow tenons which are flared about the openings of an adjacent bucket tip sufficiently to enable a calculated growth and untwist of the buckets when the turbine is at speed.
Conventionally, the tenons are peened into the bucket chamfers using a reciprocating riveting tool. The riveting tool is conventionally held in the operator""s hand and the tool anvil is placed on the tenon exposed through the tip of the bucket. A large backing plate is manually held against the discharge side of the buckets, the bucket is pried tight to the cover and the tenon is peened until the chamfer is filled. This manual method of peening the tenons to secure the buckets and cover plates to one another is abusive on the riveting tool and the operator holding the backing plate in place. Further, not only is the riveting operation loud but there is substantial variation from tenon to tenon based on operator action. These prior manual peening methods also could not properly fill the chamfer. While certain automated riveting tools, including reciprocating, orbital and radial forming tools are available, none, to applicants"" knowledge, automatically peen a tenon as well as a tenon peened by a manual operation. Accordingly, it is desirable to provide an automated machine and methods for peening tenons for securing cover plates and adjacent bucket tips of a turbine wheel to one another.
In accordance with a preferred embodiment of the present invention, there is provided an automated tenon peening tool and methods of peening tenons to secure cover plates and adjacent bucket tips of a turbine wheel to one another and which is particularly useful on axial entry-type continuously coupled turbine buckets. As noted above, cover plates between the tips of adjacent buckets have a pair of tenons projecting from opposite sides thereof. One pair of tenons is solid and intended for peening to substantially integrally secure the cover plate to a bucket. Another pair of tenons projecting from the opposite side of the cover plate are hollow and are flared subsequent to the automated peening operation to permit calculated growth and untwist of the bucket vanes relative to one another during operation. it will be appreciated, however, that instead of a pair of tenons securing a bucket tip and cover plate to one another, the peening apparatus and method hereof may be used to join the bucket tip and cover plate with only one solid tenon on one side and a hollow tenon on the opposite side. It is an automated peening apparatus and method of operation for securing cover plates and bucket tips to one another which is the subject of this invention.
The automated peening apparatus includes a fixture having stepped surfaces for locating preassembled, unsecured bucket tips and cover plates therebetween in registration with the fixture surfaces. In a preferred embodiment, a pair of tenons project from a cover plate through openings in a bucket tip for engagement in recesses in a locator surface of the fixture to locate a pair of bucket tips and a cover plate therebetween relative to the locator surface. The remaining stepped surfaces (two) of the fixture straddle the locator surface, and have a pair of recesses, and each receives tenons projecting from adjacent cover plates to support the preassembled bucket tips and cover plates in the fixture. Clamps, movable between open and closed positions, are movable to clamp the bucket tips and cover plates against the surfaces. With this arrangement, an opposing pair of solid tenons project from the opposite side of the cover plate through openings in an adjacent bucket tip.
Further, the fixture and peening head are carried on a first C-frame for receiving the bucket tips and cover plates between the peening tool carried by the head and fixture surfaces. The first C-frame is, in turn, releasably rotatably supported by a second C-frame suspended through an actuator from a point support whereby the peening apparatus is freely suspended and floating relative to the point support and bucket wheel undergoing fabrication. A hydraulic cylinder is carried by one leg of the first C-frame for displacing the first C-frame and peening head carried thereby relative to the bucket wheel clamped to the fixture. The actuator between the point support and the peening apparatus displaces the apparatus between raised and lowered positions to accommodate the movement of the peening head and support structure relative to the fixed bucket wheel and fixture when the peening tool is displaced for peening the second tenon after the first tenon has been peened. For example, as the peening head is raised by actuation of the hydraulic cylinder to align the peening tool with the second tenon, the actuator cylinder takes up the stack in the hook/chain caused thereby.
Where differently configured bucket wheels and buckets are employed, a different fixture is employed in a similar manner to accommodate the different sized bucket wheels. To compensate for the difference in weight of the various fixtures, the actuator and support assembly are linearly displaceable relative to one another in a horizontal direction, thereby counterbalancing the weight.
To utilize the automated peening apparatus, the cover plates and bucket tips are preassembled in unsecured relation to one another. With the bucket wheel fixed, a surface of the fixture is brought into alignment with a selected cover plate and bucket tip to enable the tenons on one side of the selected cover plate to extend through the bucket tip and engage in the locator recesses in the locator surface on the fixture. This is accomplished by manual displacement of the apparatus relative to the fixed bucket wheel. The clamps are then actuated to clamp the selected bucket tip and a pair of bucket tips straddling the selected bucket tip with the cover plates therebetween to the fixture surfaces. With the peening tool in alignment with one of the two solid tenons to be peened, the tool using a radial motion peens the tenon. Upon withdrawal of the tool, the first C-frame mounting the peening head is indexed to locate the tool head in alignment with the second tenon, while the bucket wheel and fixture remain stationary and clamped to one another. During movement of the suspended peening apparatus, the actuator displaces the peening apparatus a corresponding distance. The peening tool is then aligned with the second tenon and the second tenon is peened. The bucket wheel is then indexed and the operation is repeated until all of the solid tenons on one side of the bucket wheel have been peened. The peening apparatus is then removed and the tenons on the opposite side of the bucket wheel are flared, using other apparatus, to complete the securement of the cover plates and bucket tips to one another.
In a preferred embodiment according to the present invention, there is provided apparatus for securing a cover plate and tips of adjacent buckets of a turbine wheel to one another wherein the cover plate has a tenon projecting from each of the opposite sides thereof and through an opening formed in the respective tips of adjacent first and second buckets, comprising a fixture having a plurality of discrete surfaces for registration with side faces of the bucket tips, at least one of the surfaces having a recess for receiving an end portion of a tenon projecting from one side of a cover plate and through an opening in the tip of the first bucket for locating the cover plate and first bucket tip relative to the fixture and a peening head having a tool spaced from one fixture surface for peening an end of a tenon projecting from an opposite side of the cover plate and through an opening in the tip of a second bucket adjacent to and lying on the opposite side of the cover plate from the first bucket tip.
In a further preferred embodiment according to the present invention, there is provided apparatus for securing a cover plate and tips of adjacent buckets of a turbine wheel to one another wherein the cover plate has a tenon projecting from each of the opposite sides thereof and through an opening formed in the respective tips of adjacent first and second buckets, comprising a fixture having a plurality of discrete, generally parallel, surfaces offset from one another for registration with side faces of the adjacent first and second bucket tips and locating the cover plate and the first and second bucket tips relative to the fixture, a peening head having a tool spaced from the fixture for peening an end of a tenon projecting from an opposite side of the over plate and through an opening in the tip of a second bucket adjacent to and lying on the opposite side of the cover plate from the first bucket tip.
In a further preferred embodiment according to the present invention, there is provided in an apparatus including a fixture having a surface for registration with a side face of a first bucket tip of a first bucket and a guide for locating the first bucket tip and surface relative to one another, the surface lying in opposition to a peening tool for peening end portions of a tenon projecting from one side of a cover plate through an opening in a second tip of a second bucket adjacent the first bucket wherein the cover plate lies between first and second tips of the first and second buckets, respectively, a method of securing the cover plate between the first and second buckets, comprising (a) locating the tip of the first bucket in opposition to the fixture surface utilizing the guide to locate the fixture surface and the tip of the first bucket and the cover plate relative to one another and (b) peening a tip portion of the tenon projecting from the one side of the cover plate through the opening in the second tip of the second bucket by engaging the peening tool and the tenon tip to secure the cover plate and the second bucket to one another.